1. Field of the Invention
The present invention relates to a modulation method, modulator, transmission apparatus and recording medium, and more particularly to a modulation method and modulator in which a p-bit input data word is converted to a q-bit (q greater than p) code word using plural coding tables so as to intensify coding rate accompanied by increased density and a code word string is produced by coupling the code words directly, and a transmission apparatus for transmitting the code word string and a recording medium in which the code word string is recorded.
2. Description of the Related Art
Generally, the pit length to be recorded in an optical disk has a restriction about the minimum run length (minimum pit or land length) due to optical transmission characteristic for recording and reproduction and physical restraint relating to pit generation and further, a restriction about the maximum run length (maximum pit or land length) for the reason of facilitation of clock generation. Further, because of protection of a servo band and the like, it is necessary to modulate digital signals to be recorded so as to have a suppression characteristic for low-pass components thereof.
As a conventional modulation method which satisfies these restrictions in which the minimum run length is 3T (T is a period of channel bit herein after) and the maximum run length is 11T, EFM (8 to 14 modulation) method used in compact disk (CD), EFM+ method used in digital versatile disk (DVD) and the like have been well known.
In the EFM modulation used for compact disk (CD), inputted 8-bit (1 byte) digital data is converted to 14-bit run length limited code (RLL code) which satisfies a run length restriction such that its minimum run length is 3T while its maximum run length is 11T and further, 3-bit connection bit for digital sum value (DSV) control and run length restriction rule holding is attached between the converted code words so as to generate EFM modulated signals.
Regarding the minimum run length of 3T, at least two xe2x80x9c0xe2x80x9ds (number d of xe2x80x9c0xe2x80x9d) are included between logical values xe2x80x9c1xe2x80x9d and xe2x80x9c1xe2x80x9d in code words, while regarding the maximum run length of 11T, 10 xe2x80x9c0xe2x80x9ds maximum (number k of xe2x80x9c0xe2x80x9d) are included between logical values xe2x80x9c1xe2x80x9d and xe2x80x9c1xe2x80x9d in code words. The 3-bit connection bit provided for DSV control and run length restriction rule holding in order to reduce DC component and low-pass component of the modulated signal is connected between the 14-bit code words, so that the EFM modulated signal can satisfy the run length restriction rule RLL(d, k)=RLL(2, 10) that the minimum run length is 3T while the maximum run length is 11T.
Next, in the EFM+ method used for digital versatile disk (DVD), inputted 8-bit digital data is converted to a 16-bit code word and by connecting these code words directly without use of any connection bit, 8 to 16 modulation is executed so as to satisfy the run length restriction rule RLL(2, 10) that the minimum run length is 3T while the maximum run length is 11T.
Further, such a modulation method which has a higher coding rate in order to achieve a higher density recording and satisfies a run length restriction rule that the minimum run length is 3T while the maximum run length is 11T has been proposed in Japanese Patent Application Laid-Open No.2000-286709 by this applicant. According to the modulation method proposed by this applicant, for example, seven coding tables are employed for an inputted digital signal (inputted data word) in order to convert the inputted digital signal to a code word. These seven coding tables have code words corresponding to the inputted digital signal and status information for selecting a coding table for encoding a next digital signal. Signals obtained by NRZI-modulating a code word based on a specific coding table for a predetermined input digital signal and a code word based on another specific coding table have opposite polarities (even/odd parities of xe2x80x9c1xe2x80x9d are different). Consequently, for example, it is possible to convert the 8-bit data to 15-bit code word while controlling its digital sum value (DSV).
FIG.1 shows major portions of the aforementioned seven coding tables. The seven coding tables corresponding to seven statuses, status xe2x80x9c0xe2x80x9d to status xe2x80x9c6xe2x80x9d shown in the same Figure store the code word (that is, output code word after conversion) and status information indicating a coding table for use in modulating next inputted data in order to obtain a next code word which satisfies a predetermined run length restriction rule (for example, minimum run length is 3T and maximum run length is 11T) even if it is coupled with the aforementioned code word directly, corresponding to an input word. Code words corresponding to each predetermined input word are determined such that signals obtained by NRZI-converting the respective code words have polarities opposite to each other. That is, the quantities of xe2x80x9c1xe2x80x9d in respective code words corresponding to a predetermined input word have an even/odd relation such that the number of xe2x80x9c1xe2x80x9d in one code word is even while that in the corresponding code word is odd, thereby enabling the DSV control.
Although the aforementioned 16-bit code word EFM+ method can increase the coding rate by about 6% as compared to the EFM method based on 17-bit code word including a margin bit, it is desirable to improve the coding rate further in order to achieve a higher density recording.
Accordingly, the applicant proposes a modulation method which achieves a higher coding rate than the aforementioned EFM+ method while suppressing the low-pass component of a recorded signal with allocation of the code words without use of the margin bit between the code words through the aforementioned Japanese Patent Application Laid-Open No.2000-286709. However, because the number of the coding tables affects the scale of hardware upon constructing the modulator, the conventional modulator mentioned in this publication has such a problem that the scale of the hardware is too large because the seven coding tables are employed.
Accordingly, the present invention has been achieved in views of the above described problems and an object of the invention is to provide a modulation method, modulator, transmission apparatus and recording medium capable of achieving such modulation for obtaining a q-bit (q greater than p) code word from a p-bit inputted data word while a predetermined run length restriction rule is satisfied, with a small scale hardware using fewer coding tables than conventionally.
Further, another object of the present invention is to provide a modulation method, modulator, transmission apparatus and recording medium capable of further suppressing low-pass components in modulated signals in the 8-15 modulation method using no margin bit between the codes, by optimizing the coding table based on information about appearance frequency of input data words so as to achieve a DSV control with higher performance.
To achieve the above object, according to a first aspect of the present invention, there is provided a modulation method for performing a modulation to obtain a q-bit code word from a p-bit input data word (q greater than p) using plural coding tables, wherein the plural coding tables comprise six coding tables each storing a code word and status information indicating a coding table for use in modulating a next input data word in order to obtain a next code word which satisfies a predetermined run length restriction rule even if the next code word is coupled directly with the code word, corresponding to each input data word; and in a specific coding table and another specific coding table of the six coding tables, code words stored corresponding to each predetermined input data word are determined to have an even/odd relation such that the number of xe2x80x9c1xe2x80x9d in a code word in the specific coding table is even while the number of xe2x80x9c1xe2x80x9d in a code word in the other specific coding table is odd so as to enable DSV control; and upon modulating the predetermined input data word, a code word which satisfies the predetermined run length restriction rule is outputted while the DSV control is carried out by referring to the six coding tables.
According to the first aspect, the p-bit input data can be modulated to obtainq-bit code word using fewer coding tables than conventionally necessary.
According to a second aspect of the present invention, there is provided a modulation method wherein upon performing a modulation to obtain a q-bit code word from a p-bit input data word (q greater than p) using plural coding tables, each coding table stores a code word and status information indicating a coding table for use in modulating a next input data word in order to obtain a next code word which satisfies a predetermined run length restriction rule even if the next code word is coupled directly with the code word, corresponding to each input data word; and in a specific coding table and another specific coding table of the plural coding tables, code words stored corresponding to each predetermined input data word are determined to have an even/odd relation such that the number of xe2x80x9c1xe2x80x9d in a code word in the specific coding table is even while the number of xe2x80x9c1xe2x80x9d in a code word in the other specific coding table is odd so as to enable DSV control; and upon modulating the predetermined input data word, a code word which satisfies the predetermined run length restriction rule is outputted while the DSV control is carried out by referring to the plural coding tables, the modulation method comprising: obtaining the appearance frequency of each input data preliminarily; replacing code words and status informations allocated corresponding to input data words of a number set up preliminarily in succession from the highest appearance frequency to a lower one in one or more coding tables of the plural coding tables, with code words and status informations allocated corresponding to other input data words in the same coding table so as to reduce a DSV value of a code word series; and modulating the input data word using the plural coding tables including the one or more coding tables each whose code word and status table are replaced.
According to the second aspect, the code words and status informations allocated corresponding to input data words of a number set up preliminarily in succession from the highest appearance frequency to a lower one in at least one coding table are replaced with other code words and status informations allocated corresponding to other input data words in the same coding table, and a code word of q bits (for example, 15 bits) obtained by modulating a p-bit (for example, 8 bits) input data word from plural coding tables including one or more coding tables each whose code word and status information are replaced is outputted under the DSV control, so that an input data word having the highest appearance frequency can be modulated to a code word expressed by repetition of shorter pit/land than conventionally.
According to a third aspect of the present invention, there is provided a modulator wherein upon performing a modulation to obtain a q-bit code word from a p-bit input data word (q greater than p) using plural coding tables, the plural coding tables comprise six coding tables each storing a code word and status information indicating a coding table for use in modulating a next input data word in order to obtain a next code word which satisfies a predetermined run length restriction rule even if the next code word is coupled directly with the code word, corresponding to each input data word; and in a specific coding table and another specific coding table of the six coding tables, code words stored corresponding to each predetermined input data word are determined to have an even/odd relation such that the number of xe2x80x9c1xe2x80x9d in a code word in the specific coding table is even while the number of xe2x80x9c1xe2x80x9d in a code word in the other specific coding table is odd so as to enable DSV control; and a modulated code word which satisfies the predetermined run length restriction rule is outputted while the DSV control is carried out by referring to the six coding tables, the modulator comprising: a detecting portion for detecting whether a current output code word is uniquely determined or there is any option based on the input data word and the status information determined by a preceding output code word; an address computing portion which has the six coding tables, and if a detection result from the detecting portion is presence of an option, computes plural kinds of addresses of the six coding tables and outputs plural code words corresponding to the input data word from coding tables having the respective computed addresses, while if the detection result from the detecting portion is absence of any option, computes an address of one of the six coding tables including the one or more coding tables each whose code word and status information are replaced and outputs a code word corresponding to the input data word from a coding table having the computed address; and a control/output means for selecting a path having a smallest DSV value between plural paths which accumulates respective code words outputted from the address computing portion.
According to the third aspect, the p-bit input data can be modulated to obtain q-bit code word using fewer coding tables than conventionally necessary.
Further, to achieve the above object, according to a fourth aspect of the present invention, there is provided a modulator wherein upon performing a modulation to obtain a q-bit code word from a p-bit input data word (q greater than p) using plural coding tables, each coding table stores a code word and status information indicating a coding table for use in modulating a next input data word in order to obtain a next code word which satisfies a predetermined run length restriction rule even if the next code word is coupled directly with the code word, corresponding to each input data word; and in a specific coding table and another specific coding table of the six coding tables, code words stored corresponding to each predetermined input data word are determined to have an even/odd relation such that the number of xe2x80x9c1xe2x80x9d in a code word in the specific coding table is even while the number of xe2x80x9c1xe2x80x9d in a code word in the other specific coding table is odd so as to enable DSV control; and a modulated code word which satisfies the predetermined run length restriction rule is outputted while the DSV control is carried out by referring to the plural coding tables, the modulator comprising: a detecting portion for detecting whether a current output code word is uniquely determined or there is any option based on the input data word and the status information determined by a preceding output code word; an address computing portion which has the plural coding tables, wherein code words and status informations allocated corresponding to input data words of a number set up preliminarily in succession from the highest appearance frequency to a lower one in one or more coding tables of the plural coding tables are replaced with code words and status informations allocated corresponding to other input data words in the same coding table so as to reduce a DSV value of a code word series, the address computing portion, if a detection result from the detecting portion is presence of an option, computing plural kinds of addresses of the plural coding tables including the one or more coding tables each whose code word and status information are replaced and outputting plural code words corresponding to the input data word from coding tables having the respective computed addresses, while if the detection result from the.detecting portion is absence of any option, computing an address of one of the plural coding tables including the one or more coding tables each whose code word and status information are replaced and outputting a code word corresponding to the input data word from a coding table having the computed address; and a control/output means for selecting a path having a smallest DSV value between plural paths which accumulates respective code words outputted from the address computing portion.
According to the fourth aspect, like the modulation according to the second aspect of the present invention, the code words and status informations allocated corresponding to input data words of a number set up preliminarily in succession from the highest appearance frequency to a lower one in one or more coding tables are replaced with code words and status informations allocated corresponding to other input data words in the same coding table, and the code word of q bits (for example, 15 bits) obtained by modulating the p-bit (for example, 8 bits) input data word from plural coding tables including one or two or more coding tables each whose code word and status information are replaced is outputted under the DSV control, so that input data word having the highest appearance frequency can be modulated to a code word expressed by repetition of shorter pit/land than conventionally.
Further, to achieve the above object, according to a fifth aspect of the present invention, there is provided a transmission apparatus wherein upon performing a modulation to obtain a q-bit code word from a p-bit input data word (q greater than p) using plural coding tables, the plural coding tables comprise six coding tables each storing a code word and status information indicating a coding table for use in modulating a next input data word in order to obtain a next code word which satisfies a predetermined run length restriction rule even if the next code word is coupled directly with the code word, corresponding to each input data word; and in a specific coding table and another specific coding table of the six coding tables, code words stored corresponding to each predetermined input data word are determined to have an even/odd relation such that the number of xe2x80x9c1xe2x80x9d in a code word in the specific coding table is even while the number of xe2x80x9c1xe2x80x9d in a code word in the other specific coding table is odd so as to enable DSV control; and a modulated code word which satisfies the predetermined run length restriction rule is generated while the DSV control is carried out by referring to the six coding tables; and the generated code word is transmitted successively by radio or wire, the transmission apparatus comprising: a detecting portion for detecting whether a current output code word is uniquely determined or there is any option based on the input data word and the status information determined by a preceding output code word; an address computing portion which has the six coding tables, and if a detection result from the detecting portion is presence of an option, computes plural kinds of addresses of the six coding tables and outputs plural code words corresponding to the input data word from coding tables having the respective computed addresses, while if the detection result from the detecting portion is absence of any option, computes an address of one of the six coding tables including the one or more coding tables each whose code word and status information are replaced and outputs a code word corresponding to the input data word from a coding table having the computed address; and a control/output means for selecting a path having a smallest DSV value between plural paths which accumulates respective code words outputted from the address computing portion.
According to the fifth aspect of the present invention, the p-bit input data can be modulated to obtain q-bit code word using fewer coding tables than conventionally necessary for transmission.
According to a sixth aspect of the present invention, there is provided a transmission apparatus wherein upon performing a modulation to obtain a q-bit code word from a p-bit input data word (q greater than p) using plural coding tables, each coding table stores a code word and status information indicating a coding table for use in modulating a next input data word in order to obtain a next code word which satisfies a predetermined run length restriction rule even if the next code word is coupled directly with the code word, corresponding to each input data word; and in a specific coding table and another specific coding table of the six coding tables, code words stored corresponding to each predetermined input data word are determined to have an even/odd relation such that the number of xe2x80x9c1xe2x80x9d in a code word in the specific coding table is even while the number of xe2x80x9c1xe2x80x9d in a code word in the other specific coding table is odd so as to enable DSV control; and a modulated code word which satisfies the predetermined run length restriction rule is generated while the DSV control is carried out by referring to the plural coding tables; and the generated code word is transmitted successively by radio or wire, the transmission apparatus comprising: a detecting portion for detecting whether a current output code word is uniquely determined or there is any option based on the input data word and the status information determined by a preceding output code word; an address computing portion which has the plural coding tables, wherein code words and status informations allocated corresponding to input data words of a number set up preliminarily in succession from the highest appearance frequency to a lower one in one or more coding tables of the plural coding tables are replaced with code words and status informations allocated corresponding to other input data words in the same coding table so as to reduce a DSV value of a code word series, the address computing portion, if a detection result from the detecting portion is presence of an option, computing plural kinds of addresses of the plural coding tables including the one or more coding tables each whose code word and status information are replaced and outputting plural code words corresponding to the input data word from coding tables having the respective computed addresses, while if the detection result from the detecting portion is absence of any option, computing an address of one of the plural coding tables including the one or more coding tables each whose code word and status information are replaced and outputting a code word corresponding to the input data word from a coding table having the computed address; and a control/output means for selecting a path having a smallest DSV value between plural paths which accumulates respective code words outputted from the address computing portion.
Further to achieve the above object, according to a seventh aspect of the present invention, there is provided a recording medium for recording an NRZI-converted code word obtained by NRZI-converting a code word of q bits obtained by modulating p-bit input data word (q greater than p) according to six coding tables while carrying out a DSV control; each coding table storing a code word and status information indicating a coding table for use in modulating a next input data word in order to obtain a next code word which satisfies a predetermined run length restriction rule even if the next code word is coupled directly with the code word, corresponding to each input data word; in a specific coding table and another specific coding table of the six coding tables, code words stored corresponding to each predetermined input data word being determined to have an even/odd relation such that the number of xe2x80x9c1xe2x80x9d in a code word in the specific coding table is even while the number of xe2x80x9c1xe2x80x9d in a code word in the other specific coding table is odd so as to enable DSV control.
According to an eighth aspect of the present invention, there is provided a recording medium for recording an NRZI-converted code word obtained by NRZI-converting a code word of q bits obtained by modulating p-bit input data word (q greater than p) according to six coding tables while carrying out a DSV control; each coding table storing a code word and status information indicating a coding table for use in modulating a next input data word in order to obtain a next code word which satisfies a predetermined run length restriction rule even if the next code word is coupled directly with the code word, corresponding to each input data word; in a specific coding table and another specific coding table of the six coding tables, code words stored corresponding to each predetermined input data word being determined to have an even/odd relation such that the number of xe2x80x9c1xe2x80x9d in a code word in the specific coding table is even while the number of xe2x80x9c1xe2x80x9d in a code word in the other specific coding table is odd so as to enable DSV control, wherein code words and status informations allocated corresponding to input data words of a number set up preliminarily in succession from the highest appearance frequency to a lower one in one or more coding tables of the plural coding tables are replaced with code words and status informations allocated corresponding to other input data words in the same coding table so as to reduce a DSV value of a code word series, and a code word of q bits obtained by modulating p-bit input data word (q greater than p) using the plural coding tables including the one or more coding tables each whose code word and status table are replaced is NRZI-converted and recorded.
According to the eighth aspect of the present invention, it is possible to provide the recording medium in which the input data words of a number set up preliminarily from the highest appearance frequency to a lower one are recorded as code words expressed by repetition of shorter pit/land than conventionally.